pinnacle

1. (geology) A tall, sharp and craggy rock or mountain.Examples: "Kings, who remain in many respects the representatives of a vanished world, solitary pinnacles that topple over the rising waste of waters under which the past lies buried."

2. (figuratively) An all-time high; a point of greatest achievement or success.Examples: "The pinnacle of the effort to fix restrictive meanings to a set of terminology can be found in two papers in American Speech by Feinsilver (1979, 1980)."Synonyms: acme, apex, zenith, apogee, apotheosis, ascendance, capstone, climaxfiguratively

3. (architecture) An upright member, generally ending in a small spire, used to finish a buttress, to constitute a part in a proportion, as where pinnacles flank a gable or spire.Examples: "Some renowned metropolis / With glistering spires and pinnacles around."; "In the city’s midst the gleaming marble of a thousand steps climbed to the citadel where arose four pinnacles beckoning to heaven, and midmost between the pinnacles there stood the dome, vast, as the gods had dreamed it."